This application relates to a spring brake actuator wherein an indicator is provided to show when the power spring release mechanism is fully released allowing the power spring to fully expand.
In the prior art, spring brake actuators typically include an emergency or parking side enclosing a strong power spring. The emergency side selectively actuates a second pushrod in the service side of the brake actuator to set a brake. The service side is normally operated by air pressure to move its pushrod and set the brake. Under certain conditions, the emergency side may actuate the pushrod in the service side. One of those conditions would be a failure in the air system for the brake. Upon a failure of the air system, the power spring moves to set the pushrod. This locks the brake, preventing movement of the vehicle.
Under such conditions, a driver typically must cage the power spring to low the vehicle to be move. In the majority of the prior art actuators, a release bolt is associated with the spring brake actuator housing. The release bolt is moved into the emergency chamber, and pulls a threaded plate outwardly to capture or cage the power spring. In addition to these emergency situations the caging process is often utilized for shipment, repair, or other situations where the actuator is out of use for a period of time. The prior art release bolts have typically extended outwardly of the housing a significant distance to begin caging the power spring.
In addition, so-called integral release bolts have been received in the brake actuator housing. The integral release bolts are typically turned and move outwardly of the housing as they cage the power spring.
More recently, proposals have been made for a release tool that does not move outwardly of the brake actuator as it cages the power spring. The brake actuators are typically mounted beneath vehicles, and are often in a crowded space. The mounting of the brake actuator relative to other structure on the vehicle is such that there is often not enough room for the release bolt to extend outwardly of the brake actuator. At least one proposed brake actuator has included a structure wherein the release tool does not extend outwardly of the housing as the power spring is caged. Such a structure is disclosed in U.S. patent application Ser. No. 08/515,239, filed Aug. 15, 1995. In this structure, which is owned by the Assignee of the present application, and which includes one co-inventor, a threaded bolt is turned in the outer housing of the brake actuator. The threaded bolt moves a nut within the brake actuator axially towards an outer end of the brake actuator. The nut abuts and begins to move a structure which cages the power spring. The release tool, here the threaded bolt, does not move outwardly of the brake housing. Thus, there is no additional space required outwardly of the brake actuator for caging the power spring.
With such structures, new challenges arise. In the prior art release bolts, one typically knew when the spring was fully released. In particular, if a separate release bolt was removed from the brake actuator, then the power spring was fully released. When an integral release bolt was used, one knew the release bolt had fully released the power spring when the bolt abutted the outer housing.
With the recent inventions of internal release tools that do not move outwardly of the housing, however, the possibility does exist of the release tool not fully releasing the power spring release mechanism. If the power spring is not fully released, then the stroke of the emergency side is reduced, which may be undesirable.